Issue 2 of our Specification and Selection reference series deals with the surface of tile and how it impacts the selection process. If you missed the foundational Issue i.01 on body selection make sure to check it out.
The tile's surface is what we interact with on a daily basis, determines technical factors, durability and a ton of other things so as you can guess, selecting the right surface is critical to the success and longevity of your project! For now, we will constrain ourselves to looking at the functional components of the surface but don't worry - for you design aficionados, there will be lots of content to come dealing with aesthetics in future instalments.
Basics - Glaze or Unglazed
This is why we've dealt with body first because the first choice we need to make is whether you want a glazed or unglazed product. If it's unglazed, then the available porosity of the body will impact the performance, cleanability and stain resistance of your installation. There are a whole host of reasons to use an unglazed product but the primary one is a technical requirement of heavy-use areas like airports, shopping centres and commercial kitchens - deep abrasion resistance.
Deep abrasion resistance means that a substantial portion of the tile's thickness can be worn away while the overall aesthetic is retained. Let's be clear about that - Deep abrasion resistance is required when ALMOST EVERY TILE will experience hard abuse and damage from impacts or abrasion.
What it's NOT for...
This has to be one of the most common misconceptions we hear almost daily from clients. One of the key inherent benefits of ceramic products is that they are not susceptible to fading from UV exposure. Meaning, tile is one of the few cladding materials that can be spot repaired even decades down the road*. This is generally heard from homeowners in relation to their kitchen flooring. Unglazed product requires more maintenance and is susceptible to staining so why put that in your home when you don't need to? Of course, there are aesthetic reasons to select an unglazed product but like we said, we'll get into those another time.
*Pro Tip: Always make sure to order a few extra boxes of material from your project's specified material to keep in reserve. We call it "Murphy Stock" for when Murphy's law rears its head. If you have material reserved from your dye-lot, you can always do spot repairs in the case of accidents or plumbing/electrical failures.
Glazes open up a cornucopia of options in terms of technical characteristics and performance. Because glazes are primarily composed of glass (which has a porosity of 0%) they form an impervious protection layer for the tile's body as well as serving as the decorative layer.
For walls, the type of glaze doesn't have nearly the same requirements as flooring installs. Most glazes are suitable for any wall area, even wet environments. When used on floors, you want to check the PEI rating.
PEI rating is an abrasion resistance or traffic rating for flooring. There are 6 PEI classifications of glazes but for the most part we are only concerned with 3 of them. The test works by revolutions of a heavily abrasive material in contact with the tile's surface. See the table below and as usual we're going to make things simple to understand for specification purposes:
Class 0 - Wall only - extremely delicate - 100 revolutions
Class 1 - All Walls - 150 revolutions
Class 2 - Barefoot floors (ensuite baths only) - 600 revolutions
Class 3 - Any residential floor - 1500 revolutions
Class 4 - Light - Medium Commercial floors with moderate soiling - up to 12,000 revolutions
Class 5 - Heavy Commercial or aggressive soiling - over 12,000 revolutions and passes stain test after abrasion.
Pro Tip: It's important to note that this is a visual test, so lighter colors will generally have a higher PEI rating than darker colors within the same series using the same glaze. Our eyes see variance more easily in a saturated or darker color than we do in washed out or lighter colors. For heavy traffic areas, or where abrasive soil is likely (think beach house entries) lighter is better.
Since we interact with the surface of our cladding materials most, there is a lot to cover here. We'll split this post into two entries. The next one will deal with more technical issues like slip resistance, photo-catalytic oxides within glazes and more. Stay tuned and let us know if you find reference topics like this handy!
~ The Centanni Tile Team